diff --git a/AnkiServer/importer.py b/AnkiServer/importer.py
index 2c33f4c..ece6dda 100644
--- a/AnkiServer/importer.py
+++ b/AnkiServer/importer.py
@@ -6,6 +6,8 @@ from anki.importing.supermemo_xml import SupermemoXmlImporter
 from anki.importing.mnemo import MnemosyneImporter
 from anki.importing.pauker import PaukerImporter
 
+__all__ = ['get_importer_class', 'import_file']
+
 importers = {
   'text': TextImporter,
   'apkg': AnkiPackageImporter,
@@ -19,11 +21,80 @@ def get_importer_class(type):
     global importers
     return importers.get(type)
 
-def import_file(importer_class, col, path):
+def import_file(importer_class, col, path, allow_update = False):
     importer = importer_class(col, path)
 
+    if allow_update:
+        importer.allowUpdate = True
+
     if importer.needMapper:
         importer.open()
 
     importer.run()
 
+#
+# Monkey patch anki.importing.anki2 to support updating existing notes.
+# TODO: submit a patch to Anki!
+#
+
+def _importNotes(self):
+    # build guid -> (id,mod,mid) hash & map of existing note ids
+    self._notes = {}
+    existing = {}
+    for id, guid, mod, mid in self.dst.db.execute(
+        "select id, guid, mod, mid from notes"):
+        self._notes[guid] = (id, mod, mid)
+        existing[id] = True
+    # we may need to rewrite the guid if the model schemas don't match,
+    # so we need to keep track of the changes for the card import stage
+    self._changedGuids = {}
+    # iterate over source collection
+    add = []
+    dirty = []
+    usn = self.dst.usn()
+    dupes = 0
+    for note in self.src.db.execute(
+        "select * from notes"):
+        # turn the db result into a mutable list
+        note = list(note)
+        shouldAdd = self._uniquifyNote(note)
+        if shouldAdd:
+            # ensure id is unique
+            while note[0] in existing:
+                note[0] += 999
+            existing[note[0]] = True
+            # bump usn
+            note[4] = usn
+            # update media references in case of dupes
+            note[6] = self._mungeMedia(note[MID], note[6])
+            add.append(note)
+            dirty.append(note[0])
+            # note we have the added the guid
+            self._notes[note[GUID]] = (note[0], note[3], note[MID])
+        else:
+            # update existing note
+            newer = note[3] > mod
+            if self.allowUpdate and self._mid(mid) == mid and newer:
+                localNid = self._notes[guid][0]
+                note[0] = localNid
+                note[4] = usn
+                add.append(note)
+                dirty.append(note[0])
+            else:
+                dupes += 1
+
+    if dupes:
+        self.log.append(_("Already in collection: %s.") % (ngettext(
+            "%d note", "%d notes", dupes) % dupes))
+    # add to col
+    self.dst.db.executemany(
+        "insert or replace into notes values (?,?,?,?,?,?,?,?,?,?,?)",
+        add)
+    self.dst.updateFieldCache(dirty)
+    self.dst.tags.registerNotes(dirty)
+
+from anki.importing.anki2 import Anki2Importer, MID, GUID
+from anki.lang import _, ngettext
+Anki2Importer._importNotes = _importNotes
+Anki2Importer.allowUpdate = False
+
diff --git a/tests/test_importer.py b/tests/test_importer.py
new file mode 100644
index 0000000..448f534
--- /dev/null
+++ b/tests/test_importer.py
@@ -0,0 +1,113 @@
+
+import os
+import shutil
+import tempfile
+import unittest
+
+import mock
+from mock import MagicMock, sentinel
+
+import AnkiServer
+from AnkiServer.importer import get_importer_class, import_file
+
+import anki.storage
+
+# TODO: refactor into some kind of utility
+def add_note(col, data):
+    from anki.notes import Note
+
+    model = col.models.byName(data['model'])
+
+    note = Note(col, model)
+    for name, value in data['fields'].items():
+        note[name] = value
+
+    if data.has_key('tags'):
+        note.setTagsFromStr(data['tags'])
+
+    col.addNote(note)
+
+class ImporterTest(unittest.TestCase):
+    def setUp(self):
+        self.temp_dir = tempfile.mkdtemp()
+        self.collection_path = os.path.join(self.temp_dir, 'collection.anki2')
+        self.collection = anki.storage.Collection(self.collection_path)
+
+    def tearDown(self):
+        self.collection.close()
+        self.collection = None
+        shutil.rmtree(self.temp_dir)
+ 
+
+    # TODO: refactor into a parent class
+    def add_default_note(self, count=1):
+        data = {
+            'model': 'Basic',
+            'fields': {
+                'Front': 'The front',
+                'Back': 'The back',
+            },
+            'tags': "Tag1 Tag2",
+        }
+        for idx in range(0, count):
+            add_note(self.collection, data)
+            self.add_note(data)
+
+    def test_resync(self):
+        from anki.exporting import AnkiPackageExporter
+        from anki.utils import intTime
+
+        # create a new collection with a single note
+        src_collection = anki.storage.Collection(os.path.join(self.temp_dir, 'src_collection.anki2'))
+        add_note(src_collection, {
+            'model': 'Basic',
+            'fields': {
+              'Front': 'The front',
+              'Back': 'The back',
+            },
+            'tags': 'Tag1 Tag2',
+        })
+        note_id = src_collection.findNotes('')[0]
+        note = src_collection.getNote(note_id)
+        self.assertEqual(note.id, note_id)
+        self.assertEqual(note['Front'], 'The front')
+        self.assertEqual(note['Back'], 'The back')
+
+        # export to an .apkg file
+        dst1_path = os.path.join(self.temp_dir, 'export1.apkg')
+        exporter = AnkiPackageExporter(src_collection)
+        exporter.exportInto(dst1_path)
+
+        # import it into the main collection
+        import_file(get_importer_class('apkg'), self.collection, dst1_path)
+
+        # make sure the note exists
+        note = self.collection.getNote(note_id)
+        self.assertEqual(note.id, note_id)
+        self.assertEqual(note['Front'], 'The front')
+        self.assertEqual(note['Back'], 'The back')
+
+        # now we change the source collection and re-export it
+        note = src_collection.getNote(note_id)
+        note['Front'] = 'The new front'
+        note.tags.append('Tag3')
+        note.flush(intTime()+1)
+        dst2_path = os.path.join(self.temp_dir, 'export2.apkg')
+        exporter = AnkiPackageExporter(src_collection)
+        exporter.exportInto(dst2_path)
+
+        # first, import it without allow_update - no change should happen
+        import_file(get_importer_class('apkg'), self.collection, dst2_path)
+        note = self.collection.getNote(note_id)
+        self.assertEqual(note['Front'], 'The front')
+        self.assertEqual(note.tags, ['Tag1', 'Tag2'])
+
+        # now, import it with allow_update=True, so the note should change
+        import_file(get_importer_class('apkg'), self.collection, dst2_path, allow_update=True)
+        note = self.collection.getNote(note_id)
+        self.assertEqual(note['Front'], 'The new front')
+        self.assertEqual(note.tags, ['Tag1', 'Tag2', 'Tag3'])
+
+if __name__ == '__main__':
+    unittest.main()
+
diff --git a/tests/test_rest_app.py b/tests/test_rest_app.py
index 25730da..15aa53a 100644
--- a/tests/test_rest_app.py
+++ b/tests/test_rest_app.py
@@ -129,6 +129,7 @@ class CollectionTestBase(unittest.TestCase):
         shutil.rmtree(self.temp_dir)
         self.mock_app.reset_mock()
 
+    # TODO: refactor into some kind of utility
     def add_note(self, data):
         from anki.notes import Note
 
@@ -143,6 +144,7 @@ class CollectionTestBase(unittest.TestCase):
 
         self.collection.addNote(note)
 
+    # TODO: refactor into a parent class
     def add_default_note(self, count=1):
         data = {
             'model': 'Basic',